Flavonoids in Fruits, Vegetables May Lower Lung Cancer Risk

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American Cancer Society - February 25 2000

http://www2.cancer.org/zine/dsp_StoryIndex.cfm?fn=001_02252000_0

 

Eating plenty of foods rich in natural substances called flavonoids may offer

protection against some forms of lung cancer, according to a study published

recently in the Journal of the National Cancer Institute (Vol. 92, No. 2).

 

Flavonoids are plant chemicals that give a wide variety of fruits and vegetables

their unique flavors.

 

Researchers led by Loic Le Marchand, MD, of the University of Hawaii’s Cancer

Research Center, conducted interviews between 1992 and 1997 to compare in detail

the food intake of 582 people diagnosed with lung cancer to the food intake of

the same number of randomly-selected Hawaiians who did not have cancer.

 

The researchers found lung cancer risk was lowered by 40 to 50 percent among the

people who ate the most apples, white grapefruit, and onions compared to those

who ate the least amounts of those foods. Those foods contain high amounts of

the flavonoids quercetin and naringin.

 

Like the best-known flavonoid, beta-carotene, which gives carrots their color

and flavor, many flavonoids have antioxidant properties. Antioxidants are

thought to reduce the risk of some cancers. But the researchers believe

flavonoids may protect in another way – by disarming cell enzymes that transform

potentially dangerous chemicals into cancer-causing chemicals that damage a

cell’s DNA.

 

" Many of the chemicals which can cause cancer don’t do so directly, but need

activation by cell enzymes before they can start the process that leads to

cancer, " said Dr. Le Marchand. " And some flavonoids may suppress the activity of

those enzymes. "

 

It’s important to remember this study found the foods themselves were associated

with lower cancer risk, not the individual flavonoids, said Dr. Le Marchand.

More research will be needed to learn if the flavonoids alone might be

responsible for the lower cancer risk.

 

" Many nutrition researchers believe that fruits and vegetables contain a number

of protective [chemicals] that may act together to protect against disease, "

said Dr. Le Marchand. " And it may be that not all the flavonoids and their

sources are known yet. For that reason, it’s important to eat a wide variety of

fruits and vegetables, including apples, grapefruit and onions, on a regular

basis, " he added.

 

David Ringer, PhD, MPH, scientific program director at the American Cancer

Society (ACS), agrees. " There are at least 4,000 known flavonoid compounds in

fruits and vegetables, and to try to conclude that the beneficial effects of

these compounds in fruits and vegetables are due to just one or two specific

flavonoids is very difficult; the proof is just not there. "

 

Both Dr. Le Marchand and Dr. Ringer suggest following the ACS nutrition

guidelines, which call for eating at least five servings of fruits and

vegetables a day to reduce risk of cancer. A medium-sized apple, banana, or

orange equals one serving of fruit, as does three-quarters of a cup of fruit

juice or a half-cup of chopped, cooked, or canned fruit. A cup of raw leafy

vegetables equals one serving of vegetables – and you can get a serving by

having a half-cup of chopped vegetables, or three-quarters of a cup of vegetable

juice.

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